1. Field of the Invention
The present invention relates to a primary radiator for allowing a pair of probes disposed in a waveguide to selectively extract a vertically polarized wave and a horizontally polarized wave which are orthogonal to each other, and in particular, to a primary radiator having the pair of probes formed on a circuit board partly disposed in the waveguide.
2. Description of the Related Art
For example, in a satellite-television converter for receiving a left-hand circularly polarized wave and a right-hand circularly polarized wave transmitted for a satellite, the left-hand and right-hand circularly polarized waves are introduced into a waveguide and are converted into a vertically polarized wave and a horizontally polarized wave, respectively, at a 90-degree shifter, a pair of probes selectively extracts these polarized waves, and a converter circuit of the converter converts the frequencies of the received signals from the probes into signals having intermediate frequencies, thus allowing the converter to output the frequency-converted signals. By disposing the two probes apart from each other by a distance of about xcex/4, where xcex is the wavelength in the waveguide, in the axial direction of the waveguide, there is provided an advantage on one hand in that sufficient isolation between the vertically and horizontally polarized waves is achieved, and there is provided a disadvantage on the other hand in that the primary radiator constituting the waveguide becomes longer in the axial direction thereof, thus hampering attempts to miniaturize the primary radiator. By disposing the two probes in a single plane which lies in the waveguide and which is orthogonal to the axis of the waveguide, there is provided an advantage on one hand in that the waveguide can be shortened in the axial direction thereof, and there is provided a disadvantage on the other hand in that sufficient isolation between the vertically and horizontally polarized waves is not achieved, thus giving rise to a problem of deteriorated cross polarization characteristics of these polarized waves.
As shown in FIG. 5, an exemplary configuration of the known probes is such that a waveguide 10 has a circuit board 11 disposed therein, which is orthogonal to the axis of the waveguide 10, and a cylindrical stub 10a disposed in a projecting manner on the terminal face thereof, and the circuit board 11 has a probe 12 and a probe 13, formed by patterning, on the same surface thereof for the vertically and horizontally polarized waves, respectively. In a primary radiator having such probes, the two probes 12 and 13 are formed by patterning on the same surface of the circuit board 11, thereby allowing the waveguide 10 to be shortened in the axial direction thereof, and moreover, the stub 10a disposed in a projecting manner on the terminal face of the waveguide 10 achieves sufficient isolation between the vertically and horizontally polarized waves.
As shown in FIG. 6, another exemplary configuration of the known probes is such that a fine radiation pattern 14 is formed in place of the above stub 10a on the same surface of the circuit board 11 as that on which the probes 12 and 13 are formed. This fine radiation pattern 14 is square or circular and is symmetrical relative to each of the axes of the probes 12 and 13. In the primary radiator having such probes, the fine radiation pattern 14 achieves sufficient isolation between the vertically and horizontally polarized waves while providing an advantage in that the waveguide 10 is shortened in the axial direction thereof.
However, the probe configuration shown in FIG. 5 has a problem in that forming an elongated stub on the terminal face of the waveguide in a projecting manner makes the waveguide structure complicated, and in particular, when the waveguide is formed from a metal plate, this makes it extremely difficult to form the stub on the metal plate. On the other hand, although there is provided an advantage in that eliminating the above stub makes the waveguide structure simple, the probe configuration shown in FIG. 6 has a problem in that a smaller size, i.e., a smaller area of the fine radiation pattern, leads to insufficient isolation between the vertically and horizontally polarized waves, thereby making it difficult to achieve excellent cross-polarization characteristics for these polarized waves; on the other hand, a larger size of the fine radiation pattern leads to increased reflection of the these polarized waves at the fine pattern, thereby resulting in increased transmission losses.
In view of the above background of the related art, it is an object of the present invention to provide a primary radiator which can be compact and simple, while achieving sufficient isolation between the vertically and horizontally polarized waves.
To achieve the above object, a primary radiator according to the present invention comprises the following elements: a waveguide for transmitting a vertically polarized wave and a horizontally polarized wave which are orthogonal to each other; a circuit board disposed in the waveguide so as to be orthogonal to the axis of the waveguide; a fine radiation pattern formed on the circuit board in the vicinity of the axis of the waveguide; and a first probe and a second probe formed on the circuit board and extending from the inner wall of the waveguide toward the fine radiation pattern. The first probe and the second probe are substantially orthogonal to each other, and the fine radiation pattern is electrically slanted at about 45 degrees relative to each of the axes of the first probe and the second probe.
In the primary radiator configured as described above, by disposing the fine radiation pattern formed on the circuit board so as to be electrically slanted at about 45 degrees relative to each of the axes of the first and second probes, the fine radiation pattern prevents the electric field of the vertically and horizontally polarized waves in the waveguide from being disturbed, thus leading to a reduction in reflection of these polarized waves thereat while maintaining sufficient isolation between these polarized waves.
In the primary radiator having above configuration, the fine radiation pattern may have a strip shape, such as a rectangular shape and an elliptical shape, extending along a direction slanted at about 45 degrees relative to each of the axes of the first probe and the second probe. Alternatively, the fine radiation pattern may have an L-shape having a first arm and a second arm which are substantially orthogonal to each other and which are electrically slanted at about 45 degrees relative to each of the axes of the first probe and the second probe.
Thus, the present invention has the following advantages.
A circuit board is disposed in a waveguide, in which a vertically polarized wave and a horizontally polarized wave propagate, so as to be orthogonal to the axis of the waveguide, has a first probe and a second probe formed thereon for respectively extracting the vertically and horizontally polarized waves, and also has a fine radiation pattern formed thereon electrically slanted at about 45 degrees relative to each of the axes of the first and second probes. This configuration allows a fine radiation pattern having a relatively small size to prevent the electric field of the vertically and horizontally polarized waves in the waveguide from being disturbed and also these polarized waves from being reflected thereat, while maintaining sufficient isolation between these polarized waves.